Muon (g-2) Technical Design Report (1501.06858v2)

Abstract: The Muon (g-2) Experiment, E989 at Fermilab, will measure the muon anomalous magnetic moment a factor-of-four more precisely than was done in E821 at the Brookhaven National Laboratory AGS. The E821 result appears to be greater than the Standard-Model prediction by more than three standard deviations. When combined with expected improvement in the Standard-Model hadronic contributions, E989 should be able to determine definitively whether or not the E821 result is evidence for physics beyond the Standard Model. After a review of the physics motivation and the basic technique, which will use the muon storage ring built at BNL and now relocated to Fermilab, the design of the new experiment is presented. This document was created in partial fulfiLLMent of the requirements necessary to obtain DOE CD-2/3 approval.

Overview of the Muon g-2 Technical Design Report

The "Muon g-2 Technical Design Report" is a comprehensive document detailing the planning, execution, and anticipated outcomes of the Muon g-2 experiment at Fermilab. It represents a collaborative effort of global scientific institutions with the primary objective of measuring the muon anomalous magnetic moment, $a_\mu = \frac{(g - 2)}{2}$, to an unprecedented precision of 0.14 parts per million (ppm). This level of precision is crucial for comparing experimental results with the Standard Model (SM) predictions and potentially unearthing discrepancies that could indicate new physics.

Experimental Design

The experiment builds on the previous success of the E821 experiment conducted at Brookhaven, which reported a significant deviation between the measured and predicted values of $a_\mu$. This anomaly suggested potential physics beyond the SM, encompassing theories such as supersymmetry and dark sector interactions.

Central to the Fermilab experiment are several existing and enhanced facilities. The storage ring, first developed for the E821 experiment, will be transported and reassembled at Fermilab. This ring facilitates a unique environment for accurately resolving the spin precession of muons as they circulate the ring. The key challenge addressed involves integrating precise magnetic field measurements, employing sophisticated Nuclear Magnetic Resonance (NMR) probes to achieve field uniformity at sub-ppm levels.

Beamlines and Accelerator Complex

The experiment capitalizes on Fermilab's infrastructure, particularly the former Antiproton Source, which plays a crucial role in generating the required high-intensity, high-purity muon beam. Protons accelerated by the Booster are guided through various beamlines to incite pion production in a target station. The decay of selected positively charged pions results in a polarized muon beam ideal for the experiment’s objectives. Modifications are made to the Debuncher, designated as the Delivery Ring, to purify the muon stream adequately by eliminating protons through a timing separation mechanism.

The beamlines ensure precision transport of pions and muons via optimized focusing and momentum selection, crucial for limiting contaminating background particles and preserving muon polarization. These structures leverage state-of-the-art focusing techniques and advanced current-pulsed magnets to maximize the muon yield while minimizing beam aberrations.

Detectors and Data Acquisition

The report outlines the advancements in detection systems crucial for measuring the decay positrons from muons to infer spin precession frequencies. The improved calorimetry setup includes arrays of crystals and SiPM readouts, enhancing spatial resolution and energy calibration. The data acquisition (DAQ) system is designed to efficiently manage increased rates and data volumes, implementing a MIDAS-based architecture for real-time monitoring and offline analysis support.

The experimental approach incorporates the T-method for maximizing statistical power in detecting the anomaly, incorporating systematic checks, and optimizing computational resources for fast data processing and storage.

Systematic Uncertainties and Corrections

A significant portion of the report is devoted to addressing potential sources of systematic uncertainty, quantitatively similar to 0.1 ppm, such as muon beam dynamics, field non-uniformities, and EDM effects. Strategies discussed include beam collimation, enhanced tracking systems, and continuous improvements in simulation models, ensuring the corrections required for meticulous determination of $a_\mu$ are both precise and accurate.

Implications and Prospects

The completion of the Muon g-2 experiment at Fermilab holds promise for a comprehensive understanding of $a_\mu$ and, more broadly, for testing beyond-the-Standard Model theories. If the previous Brookhaven deviation holds, the results could illuminate connections to phenomena observable at the LHC or even suggest concepts yet unformulated.

This technical design report elucidates meticulous planning and design evolution, presenting a robust framework for what can be an instrumental experiment in redefining our fundamental understanding of particle physics. As technological enhancements and collaborations thrive, this experiment embodies a methodical quest to deepen insights into the fundamental forces governing the universe.